Study on mechanism and prevention technology mode of thick-hard roof induced punching in composite key stratum

The key stratum of thick-hard roof is key factor to induce coal mine impact, mine earthquake and other disasters. The disaster is more serious under the condition that the coal seam roof has the key stratum of composite thick-hard roof, which is easy to induce large-scale rock burst disaster. Aiming at the rock burst disaster induced by the composite key stratum of thick-hard roof, the mechanical model of the composite key stratum of thick-hard roof is established, the stress equation of the tensile and compressive zone of the composite key stratum roof is constructed, and the identification method of the composite key stratum roof is given. Based on the typical composite key strata roof development working face as the background, using theoretical analysis and similar simulation, reveals the composite key strata roof strata breaking characteristics, reveals the upper and lower key strata roof synchronous breaking release dynamic load disturbance superposition, induced impact disaster mechanism. The non-cooperative fracture mechanics identification conditions of the composite key layer of 'cantilever beam' and 'masonry beam' are put forward, the reasonable distance of the fracture line of the upper and lower key layers is quantitatively determined, and the prevention and control technology mode of single-layer and double-layer cooperative staged fracturing weakening and pressure relief transformation of the upper and lower key layers is created. The characteristics of stress, deformation and surrounding rock failure under different fracturing modes are studied. The disaster-inducing mechanism of thick and hard roof of composite key strata in upper and lower key strata is pointed out, and the fracture relationship of overlying strata under different fracturing modes is analyzed. The results show that the fracturing of the lower key layer mainly changes the thick-hard roof.